This invention relates to a jet pump apparatus for mixing a higher pressure gas from a higher pressure gas supply derived from a compressor stage of a gas turbine engine, which typically is an aircraft engine, and a lower pressure gas from a lower pressure gas supply in order to provide a pressurised gas supply to a downstream apparatus, such as for example only, a downstream on-board oxygen generating system, e.g. of the kind which utilises molecular sieve bed technology, or an air conditioning apparatus, or any other desired gas-using downstream apparatus.
More particularly but not exclusively the invention is for mixing higher and lower pressure gases which are produced by respective higher and lower compression stages of a gas turbine engine.